The last time I checked Ladbrokes were offering odds of something like 7/2 against Tory MP Mary Macleod holding her Brentford & Isleworth seat in the May 2015 General Election.

My view until recently was that those odds really don't do justice to Conservative chances in the constituency: I took the attitude that although the contest is probably marginally shaded in favour of Labour challenger Ruth Cadbury it might be worth risking a £200 flutter on Ms Macleod so that any last-minute national surge in Tory support would deliver me a badly-needed mini windfall.

Right now I'm glad I resisted the temptation - and not just because it might have seemed like an act of disloyalty to my own party.

In May's local & European elections Labour were around 12-13% ahead of the Tories in Brentford & Isleworth. That's a pretty hefty margin to overcome but at the time it seemed reasonable to expect that much of it would be wiped out by the customary 'swing back' that tends to occur in favour of any governing party as a general election approaches.

That much anticipated swing back may yet happen but the problem for Ms Macleod is that six months on a new constituency-wide opinion poll (commissioned, as it happens, by her former benefactor Lord Ashcroft) shows the Labour lead lengthening to 15%.

This means that she needs an 8% swing back to hold the seat whereas the lessons of historical precedent show that in the last six months of the average post-war Tory parliament the actual swing back is usually only around one half of that figure.

Of course there is the issue of Mary Macleod's personal vote. In the case of most newly-incumbent MPs this may not be a lot but it seems reasonable to expect that it could add perhaps 1-2% to her coffers.

Against this factor it has been suggested that Ruth Cadbury will benefit from the re-wind effect of the alleged profligacy of her predecessor's expense claims and that Labour is stronger in this seat that the 2010 General Election figures suggest.

This may be true but we probably shouldn't over-emphasise it because whilst Ann Keen did lose the seat by a 3.2% margin in 2010 Labour also lost the aggregate vote in the local council elections that were held in the constituency on the same day, albeit by a smaller margin. Even if the 'Keen factor' was significant the effect of its removal will already be inherent in the Ashcroft poll data.

Some say that no party can win this seat if they are committed to the expansion of Heathrow but the reality is a little more complex than that. A 'no third runway' pledge would certainly be a vote winner in Turnham Green but it might not go down so well among airport workers living in Hounslow Heath.

That said, there are probably more 'swing voters' in the anti-Heathrow areas of the constituency than there are in those heavily BME neighbourhoods that tend to favour the construction of a third runway. If true this issue may be hurting Mary Macleod because her party's anti-expansion policy no longer seems to be quite as emphatic as it was in 2010.

There are also issues of demographic change at work in this seat, though they have not all been favourable to Labour: true, there is a rising Asian vote in the West of the constituency (and this has already transformed the political balance in two wards) but the East has seen an increasing 'gentrification' in recent years.

Chiswick, which by virtue of its high turnout accounts for around one third of Brentford & Isleworth voters, is very middle class and therefore nominally Conservative for fiscal reasons. However, it is also quite 'intellectual' and really rather socially liberal.

This might help to explain why UKIP has made so little impact in the town. (In fact Chiswick Riverside Ward delivered their lowest vote in the borough in this May's local council elections). Mary Macleod's support for the Cameron project of gay equality and economic austerity will probably do her little harm in that neck of the woods.

It is significant that Labour won seats in two of the three Chiswick wards in the 1994 borough council elections whereas this year they failed to win any, despite achieving the same 11% lead across Greater London on both occasions.

That, however, was compared to a demographically-changing capital that has seen huge shifts in Labour's favour in just one generation. Whilst gentrification may have given the Tories a temporary boost in Chiswick the underlying trends relating to the ethnic composition of local schools suggest that in time the town will soon become much more electorally competitive.

As a consequence we are likely to see the constituency shift permanently into the Labour column within fifteen or twenty years from now - but that is still some way off.

Who wins in the constituency on polling day May 2015 will depend largely upon whether the Tories can claw back the type of 7-point nationwide lead which they enjoyed in the last general election. If they succeed then Mary Macleod may still have a chance of holding this. If not then Cllr Cadbury will be adding the initials 'MP' to her name.